fernandoae2017 wrote:I'd like to know what is the support status of the AT91SAM9G20 processor in vanilla kernels 4.x.

Did you inspect the mainline source tree?
Seems like that SoC (with a ARM926EJ-S processor) is actively supported just like every other SAM9 chip still in production.

FYI ETRAX SoCs (i.e. the CRIS architecture) ceased production in 2010, but there was support in mainline kernel for another eight years, until arch/cris was removed in 4.17.
Whereas the SAM9G20 is still in production, yet you have concerns?